Abstract
This paper examines the production technology of Egyptian blue, an ancient artificial pigment, through the investigation of an unsuccessfully produced pellet derived from the Hellenistic production site of Kos (Dodecanese, Greece). This heterogeneous material was investigated by a combination of laboratory and synchrotron radiation-based (SR) techniques: scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, micro-Raman spectroscopy, high-resolution SR micro-X-ray fluorescence spectroscopy, and SR micro-X-ray absorption near-edge structure spectroscopy (XANES), at the ID21 beamline of the European Synchrotron Radiation Facility. Principal component analysis of a large dataset of 171 micro-XANES spectra acquired on the archaeological samples and on a series of reference copper compounds emphasizes high variations of XANES features due to different speciation and also orientation effects, as demonstrated by the simulated XANES spectra. The results indicate that, rather than inadequate firing temperatures that could have led to the reddish cuprite (Cu2O), unsuccessful production may occur due to the use of inappropriate starting materials, which contain an unusually high iron content. The contextual interpretation underlines the intertwined relationship between the production of Egyptian blue and metallurgy.
Highlights
Introduction to the Application of MaterialsScience to Archaeometry and Conservation Science; Oxford University Press: New York, 2010.(56) Pinakidou, F.; Katsikini, M.; Paloura, E
By combining synchrotron radiation-based (SR)-micro-XRF and SR-micro-X-ray absorption near-edge structure spectroscopy (XANES) with the laboratory optical microscopy (OM), scanning electron microscopy (SEM)−energy-dispersive X-ray spectrometry (EDS), and micro-Raman spectroscopy, we were able to determine most of the phases present in the complex matrix of Egyptian blue (EB)
The XANES spectra showed that copper is predominantly present as Cu2+, pointing to an oxidizing atmosphere while firing
Summary
The XANES spectra of the commercially available EB, as measured in six different spots (Figure 5a), and a series of reference copper compounds (Supporting Information Figure S10) were recorded. To establish possible signatures in the XANES spectra, and identify the composition of Cu in the different locations selected, PCA was carried out on the entire set of normalized XANES spectra obtained from (i) six different spots of the commercial EB, (ii) the series of copper references, and (iii) the 152 spots on the four archaeological samples (Figure 5b, Supporting Information Figure S11a,b). The variance of the different XANES spectra measured on the reference EB material, which appears as PC1 (Supporting Information Figure S11a), can be explained by the differently oriented crystallites with respect to the microbeam. Such (trace) copper species are probably present as phases other than our reference compounds, where copper may even replace other ions
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